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Control of wild radish in grain with sulfuric acid. 





Introduction 3 

Commercial use of sulfuric acid as a herbicide 5 

Influence of weeds on yield of cereal crops 5 

Competition for moisture 5 

Competition for soil nutrients 5 

Competition for sunlight 5 

Increased harvest costs 6 

Weeds in waste places 6 

Preliminary experiments in field spraying 6 

Experiments on the control of weeds in grain fields 7 

Factors influencing the effectiveness of sulfuric acid as a weed spray ... 10 

Time of application 10 

Recovery of grain plants ; . 12 

Stand of grain 12 

Temperature and humidity 12 

Rain, dew, and fog 13 

Degree of weed infestation in relation to yield of grain 13 

Effect of sulfuric acid on the soil 14 

Effect of sulfuric acid on the cereal plant 14 

Eradication of mustard and wild radish from grain fields by the acid treatment 14 

Study of wetting agents or ' 'spreaders" 14 

Weed control in onions 16 

Equipment for applying sulfuric acid 17 

Effect of sulfuric acid on metals and other materials 17 

Avoiding open handling of sulfuric acid 17 

Development of ejector mixing method 18 

Equipment used in 1935 21 

Tests of the 1935 sprayer '. 24 

Conversion of a portable orchard sprayer to an acid sprayer 26 

Cost of application of acid 27 

Precautions in handling sulfuric acid 28 

Summary 28 

Acknowledgments . 29 


W. E. BALL 3 and 0. C. FRENCH 4 


For several years it has been known that dilute sufuric acid may be 
used effectively to control annual weeds. Discovery of the method 
whereby weeds in cereals could be controlled without injury to the grain 
was made in 1896 by Bonnet, a Frenchman. He found that some plants 
with broad and rough leaf surfaces and exposed growing points were 
readily killed by certain chemical sprays, whereas other plants such as 
cereals, with narrow and smooth leaves and well-protected growing 
points, were only temporarily injured. Two years later this same worker, 
cooperating with Brandin and Ducos, employed dilute sulfuric acid suc- 
cessfully as a herbicide but concluded that its practical use was im- 

In 1911, Rabate, 5 in France, initiated work on the use of dilute sul- 
furic acid for weed control. For winter cereals he recommended 10 per 
cent sulfuric acid by volume (specific gravity 1.100-1.110) used at the 
rate of 1,000 to 1,200 liters per hectare (107-128 gallons per acre) ; and 
for spring cereals 4 to 4.5 per cent by volume ( 1.040-1.045) ap- 
plied at the same rate per hectare. Morettini, 6 in Italy in 1913-15, work- 
ing with wheat, found dilute sulfuric acid to be most effective among the 
several chemicals he tested. He obtained six more bushels of grain in 
sprayed than in unsprayed areas by using the concentrations of acid and 
the volumes per hectare recommended by Rabate. 

1 Eeceived for publication August 12, 1935. 

2 This project was inaugurated and supported by the Crop Protection Institute, 
through funds contributed by the Freeport Sulphur Co., New York City. The 
California State Department of Agriculture has assisted in the promotion and 
direction of the project. 

3 Associate in the Experiment Station and Investigator for the Crop Protection 

4 Instructor in Agricultural Engineering and Junior Agricultural Engineer in 
the Experiment Station. 

s Eabate, E. Destruction des ravenelles par l'acide sulfurique. Jour. Agr. Prat, 
(n.s. 21) 75(l):407-9. 1911. 

6 Morettini, A. L'impiego dell' acido solforico per combattere le erbe infeste 
nel frumento. Staz. Sper. Agr. Ital. 48:693-716. 1915. 


4 University of California — Experiment Station 

Korsmo, 7 beginning in 1914 in Norway, has carried on the most com- 
prehensive study of weed control in grain that has been made. His 
findings, however, have not yet been widely disseminated, since until 
recently they were published only in Norwegian. By using dilute sul- 
furic acid varying in strength from 3.5 to 5 per cent by weight, and by 
using 100 liters per decare (107 gallons per acre), he obtained an in- 
creased yield of grain amounting to 20.5 per cent for spring wheat, 25.8 
per cent for barley, and 29.1 per cent for oats. The original weed 
growth was reduced by 81.8 per cent in all spring cereals by this treat- 
ment. Sulfuric acid generally gave better results than other methods 
used. These methods include weed harrowing before and after germina- 
tion of cereals, harrowing and spraying, spraying with green vitriol and 
with nitric acid, dusting with calcium cyanamide and charlock powder, 
and hand weeding. 

Aslander, 8 who has done much research in weed control both in 
Sweden and the United States, has assembled considerable data regard- 
ing the effect of sulfuric acid upon a large number of weed species 
treated. These data show that many common annual weeds are killed by 
dilute sulfuric acid. Besides doing careful work in determining the 
action of the acid on plant tissue, he has studied the influence of hu- 
midity, soil moisture, temperature, and rain on the acid treatment. He 
has found the effectiveness of sulfuric acid to be less influenced by 
weather conditions than that of iron sulfate, which until recently was 
the most popular chemical for this type of weed control. 

Brown and Streets, 9 in Arizona, recommend dilute sulfuric acid spray 
for controlling a number of weeds. Under their conditions of high tem- 
perature and low humidity they were able to use it very effectively. Best 
results were obtained by applying the solution at a pressure of 250 
pounds per square inch. 

The National Sulphuric Acid Association of England 10 has recently 
found that a "late blight" of potatoes may be successfully checked from 
descending to the tubers by dilute sulfuric acid applied to the plants at 
the proper time. This treatment kills the foliage, thus controlling the 
blight and enabling the farmer to harvest potatoes without waiting for 
the tops to die normally. 

7 Korsmo, Emil. Unders0kelser 191G— 1923. 0ver ugressets skadevirkninger og dets 
bekjempelse I Akerbruket. p. 378-94. Johansen and Nielsens Boktrykkeri, Oslo. 1932. 

s Aslander, Alfred. Sulphuric acid as a weed spray. Jour. Agr. Besearch 24(11) : 
1065-91. 1927. 

9 Brown, J. G., and R. B. Streets. Sulphuric acid spray: A practical means for 
the control of weeds. Arizona Agr. Exp. Sta. Bui. 128:299-316. 1928. 

10 National Sulphuric Acid Association, England. Agr. Dept. Bept. 1933-34: 
1-12. 1934. 

Bul. 596] Sulfuric Acid for Control of Weeds 5 


The commercial developments in the use of dilute sulfuric acid for weed 
control in numerous foreign countries indicate its value and popularity. 
Although data giving the amount applied annually as a herbicide in the 
Scandinavian countries are not available, much is used there, particu- 
larly in Norway. In France the popularity of sulfuric acid has been in- 
creasing. In 1931, 27,000 tons of concentrated acid were used for weed 
control, almost wholly in cereals ; in 1933 about 500,000 acres of cereals 
were treated. In England the National Sulphuric Acid Association 
started its investigation of this herbicide in 1931. In that year only a 
few acres of grain were sprayed ; in 1932 between 200 and 300 acres ; the 
following year about 5,570 ; and in 1934 over 20,000. 

The possibilities of sulfuric acid as a herbicide are now being investi- 
gated in South Africa, Argentina, Russia, Spain, Jamaica, India, Aus- 
tralia, New Zealand, and Canada. The last-named country has for some 
time been investigating through its National Research Council. 


In order to fully appreciate the problem which infestations of mustard 
(Brassica spp. 11 ) and wild radish (Baphanus sativus) present to grow- 
ers of small grains in California, one needs only to visit the inland 
valleys during March and April when the weeds are in blossom. In 1935 
California grew approximately 1,000,000 acres of barley, 400,000 acres 
of wheat, and 75,000 acres of oats. By conservative estimates, about 50 
per cent of this total acreage is more or less infested with either mustard 
or wild radish. 

Although accurate data on the amount of harm caused by these weed 
pests are not available, heavy losses are obvious. Among the many rea- 
sons why these weeds should be eradicated from grain fields are the 

Competition for Moisture. — In many parts of California where grain 
is grown the annual rainfall is barely sufficient to produce a good grain 
crop even in the absence of weeds. Certainly in these areas, mustard 
plants, which require much water, are a serious menace. 

Competition for Soil Nutrients. — In all cases where grain is infested 
with weeds there is a continual battle between the weeds and grain for 
plant food. Despite California's rich soils, mustard and wild radish have 
been known to starve the grain, thus reducing yield as well as quality. 

Competition for Sunlight. — Figure 1 illustrates clearly the shading 

11 The three most common mustards in California are Brassica arvensis, B. cam- 
pestris, and B. nigra, in the order given. 

6 University of California — Experiment Station 

of grain by mustard. Grain grown under such conditions is so weak and 
slender that lodging often takes place. 

Increased Harvest Costs. — Not only are the actual costs of threshing 
the grain increased ; but sometimes in severe infestation, fields are never 
harvested. The cost of cleaning the weed seed from grain, particularly 
the seed pod of wild radish, greatly decreases the net income to the 


Weeds allowed to mature along fence lines, roadsides, ditchbanks, and 
other waste places often form the principal source of an initial weed 
infestation and a continuous source of reinfestation. Aside from this 
detriment, many of these weeds harbor insect pests, which in certain 
seasons invade field crops. These weeds not only act as a source of food 
when more succulent crops are not available, but also form a shelter 
during winter months and furnish a breeding place for many insects. A 
few weeds which are known to be hosts to certain insects and susceptible 
to treatment with sulfuric acid are listed as follows : 

Weeds Insects 

Wild lettuce (Lactuca spp.) Bean thrips, aphid (several species). 

Russian thistle (Salsola kali) Sugar-beet leafhopper, western beet-leaf beetle. 

Shepherd's purse (Capsella bursa- 
pastoris) and Lamb's-quarters 

(Chenopodium album) Sugar-beet leafhopper, clover aphid, bean aphid, 

cotton or melon aphid, cabbage aphid. 

Dock (Rumex spp.) Citrus thrips, grape leafhopper, apple leafhopper, 

sugar-beet wireworm. 

Wild mustard (Brassica spp.) Sugar-beet leafhopper, grape leafhopper, onion 

thrips, sugar-beet wireworm, potato flea beetle, 
western flea beetle, hop flea beetle. 


In the first year's work (1934) a spray unit mounted on a truck was 
used. The pump was of the reciprocating type, made of bronze, the sup- 
ply tank being specially constructed of lead-lined steel. All pipes, con- 
nections, nozzles, and the like, coming in contact with the dilute acid 
were of brass. The pump could maintain 75 pounds' pressure per square 
inch on a 6-foot boom equipped with six nozzles. 

Plots of grain, of % -acre area, arranged at random, were sprayed in 
fields infested with mustard and wild radish. Five replications were 
made of each treatment. These treatments consisted of three concentra- 
tions of acid, 12 namely 5, 7.5, and 10 per cent by weight, and three vol- 
umes, 80, 120, and 160 gallons per acre. 

12 The concentrated acid used throughout these experiments was commercial 66° 

Bul, 59G] 

Sulfuric Acid for Control of Weeds 

Mustard and wild radish plants were counted during the blossoming 
period in both the treated and untreated areas to determine the percent- 
age killed by the spray. Square-yard quadrats were used, ten counts 
being made in each of the treatments. The results of experiments con- 
ducted on the El Dorado Ranch, near Knights Landing, are shown in 
table 1. For yield determinations ten samples of a square yard each were 
harvested from each treatment. 

Fig. 1. — Effect of dilute sulfuric acid spray on barley heavily infested with 
mustard. Note the shading of the grain by the mustard in the unsprayed area 


An effort was made in 1935 to develop a spray equipment satisfactory 
not only for experimental purposes but also large enough for commer- 
cial application in large fields. This equipment, which will be fully de- 
scribed later in this bulletin, was used for all applications made during 

A series of spraying demonstrations were conducted under the super- 
vision of the Agricultural Extension Service of the University of Cali- 
fornia to give the grain growers of California the benefit of the experi- 
ence gained in 1934. These applications proved further the effectiveness 
of sulfuric acid and the practicability of the equipment used under the 
varying conditions of California agriculture. Operations were conducted 
in nine of the leading grain counties of the state. 

The "randomized block" arrangement in the 1935 field experiments 


University of California — Experiment Station 

conforms with the method suggested by Fisher and Wishart. 13 One- 
tenth-acre plots were used, replicated six times. To determine the per- 
centage of weeds destroyed and the yields, a 3-foot quadrat was em- 


Percentage of Mustard Plants Killed and Calculated Yield per Acre 

Obtained by Treating Mustard-Infested Barley with 

Dilute Sulfuric Acid; 1934 

Treatment No. 


of sulfuric acid, 

by weight 

per acre 

Mustard killed 



per acre 


per cent 


per cent 
85 50 

100 pounds 
25 .43 

















30 03 
33 36 

31 91 
31 72 





15 78 






20 73 


Percentage of Mustard Plants Killed and Calculated Yield per Acre 

Obtained by Treating Mustard-Infested Barley with 

Dilute Sulfuric Acid; 1935 

Treatment No. 


of sulfuric acid, 

by weight 

per acre 

Mustard killed 



per acre 


per cent 



per cent 

100 pounds 


35 54 







6 . 

22 82 

ployed. In the counting of mustard plants, only three counts were made 
in each treatment, whereas for yield determinations five samples were 
taken from each plot. Table 2 shows the results obtained from the Cecil 
ranch, near Davis. This grain, which was heavily infested with mustard 
(Brassica arvensis), was sprayed March 27. The grain was from 2 to 3 

13 Fisher, E. A., and J. Wishart. The arrangement of field experiments and the 
statistical reduction of the results. 24 p. Imperial Bureau of Soil Science, London, 

Bul. 596] 

Sulfuric Acid for Control of Weeds 

inches high, while the mustard was mostly in the four to six-leaf stage 
of development. There was some germination of mustard seed in this 
field after the spraying took place. Figures 2 and 3 show samples of this 
grain at harvest. 

Fig. 2. — Samples of barley taken from adjoining 
plots. The bundle at the right is free from mustard. 

The results given in table 3 were obtained from a barley field also 
heavily infested with mustard {Brassica arvensis and B. campestris) , on 
River Farms property near Knights Landing. Figure 4 shows samples 
of results of two treatments on this ranch. The spraying took place on 
April 4 when the grain was 6 to 8 inches high and the mustard 4 to 6 
inches. This experiment presented an excellent example of grain-lodging 
caused by mustard. Figure 5 is from a photograph of this field at harvest. 


University of California — Experiment Station 


Time of Application. — Much has been written regarding the proper 
time for spraying mustard-infested grain fields in order to control 
weeds effectively. Under California conditions, the most satisfactory re- 

Fig. 3. — Uniform samples of barley, showing the amount of 
mustard seed in the grain from an untreated field. 


Percentage of Mustard Plants Killed and Calculated Yield per Acre 

Obtained by Treating Mustard-Infested Barley with 

Dilute Sulfuric Acid; 1935 

Treatment No. 


of sulfuric acid, 

by weight 

per acre 

Mustard killed 



per acre 


per cent 




per cent 

100 pounds 






34 30 





suits have been obtained when the earliest growth of mustard is 6 or 7 
inches high. Figure 6 shows the range of size at which mustard may be 
effectively killed with dilute acid. Mustard has been sprayed in the early 
blossoming stage without significant injury to the grain. Spraying at 
this stage, however, is not generally recommended because long periods 
of dry weather following late applications are apt to injure the grain 

Bul. 596] 

Sulfuric Acid for Control of Weeds 


Fig. 4. — Bags of barley, showing comparative yield of grain re- 
sulting from spraying with dilute sulfuric acid. The weights shown 
represent samples from 30 quadrats of one square yard each. 

Fig. 5. — Effect of sulfuric acid treatment on lodging of grain. In the center 
the treated grain is shown standing erect, while dark strips on the right and left 
of the center are unsprayed areas in which the grain and weeds are lodged. Still 
farther to the right and left are other treated strips. 


University of California — Experiment Station 

permanently. Conversely, spraying too early often results in a reinf esta- 
tion from mustard seeds germinating after the treatment. 

Because of the variation in the seasonal conditions in different parts 
of California, the period during which cereals can be sprayed with the 
acid extends from early January, in the southern counties, to late April 
in the northern counties — a total period of four months. The date will 
vary from year to year, according to the season. 

Recovery of Grain Plants. — The time required for the grain to recover 
completely from the spray depends primarily upon two factors. Of these 

Fig. 6. — Mustard plants in the best stages of development for treatment with 
sulfuric acid. The corresponding sizes of grain plants are illustrated at the right. 

the first is the stage of development of the grain at the time of applica- 
tion. Young grain, from 4 to 6 inches high, will completely recover in 7 to 
10 days ; while grain from 10 to 12 inches high when sprayed often re- 
quires from 3 to 4 weeks for complete recovery. The second factor is the 
weather following the application ; with plenty of moisture in the soil 
and with favorable growing conditions, recovery is greatly facilitated. 

Stand of Grain. — A heavy stand of grain offers considerable compe- 
tition to the young mustard plants, causing them to grow slender, with 
but few basal leaves. Under these conditions most mustard plants in 
grain are very readily destroyed with a concentration of acid as low as 
7.5 per cent by weight. These same weeds growing in a thin stand of 
grain have a tendency to "stool" and develop a very short, sturdy stalk, 
so that a 15 per cent solution of acid by weight is often necessary for 
their complete destruction. 

Temperature and Humidity. — The action of dilute sulfuric acid on 
plant tissue is more rapid on warm, dry days than on cool days. Asian- 

Bud. 596] Sulfuric Acid for Control of Weeds 13 

der 14 has made a rather comprehensive study of temperature and hu- 
midity. Using a 2 per cent solution of acid, he was able to kill plants in 
one hour at 30 degrees Centigrade, whereas at 6 degrees this same con- 
centration of acid required five hours for similar results. He found also 
that mustard plants were killed under all conditions of humidity but 
that best results were obtained in dry air. 

Bain, Dew, and Fog. — Rain falling shortly after the application will 
reduce the effectiveness of the acid. If two hours have elapsed, however, 
after the spraying, the rainfall will have no serious effect. In the event 
of threatening rain, it has been found advisable to increase the concen- 
tration of the acid and reduce the volume of solution per acre. Rain 
falling about an hour after application of acid on one of the experi- 
mental plots, in 1935, rendered the 10 per cent trial nearly worthless, 
while a 15 per cent application was very effective. The greater the con- 
centration of the solution, the more rapid the kill of the mustard plant. 

Fog and heavy dew have much the same influence as rain. When mus- 
tard plants are thoroughly wet from either fog or heavy dew, it is ad- 
visable to apply a stronger concentration, allowing the dilution to take 
place on the plants. Where, for example, under normally dry conditions 
a 10 per cent solution applied at the rate of 130 gallons per acre would 
be used, a 15 per cent solution applied at the rate of 95 gallons per acre 
under wet conditions gives similar results. 

Degree of Weed Infestation in Relation to Yield of Grain. — Several 
investigators maintain that sulfuric acid has a fertilizing effect on the 
cereal. Frequent large differences in yield between the sprayed and un- 
sprayed grain would lead one to believe such to be the case. The limited 
data available indicate, however, that the differences in yield are di- 
rectly related to the degree of weed infestation. In other words, if a field 
heavily infested with mustard or wild radish is sprayed, a reasonably 
large increase in yield may be expected ; on the other hand, little differ- 
ence can be expected from spraying light infestations. The question 
naturally arises as to the degree of infestation that will justify sulfuric 
acid treatment. This question can best be answered if the purpose in the 
mind of the grower is known. If the control of weeds from the standpoint 
of future infestations is considered, lightly infested fields may well be 
sprayed. If, however, the thought is of the economic gain on one year's 
crop only, then of course the acid will be applied only to the more heavily 
infested fields. Where pulling by hand is impossible because of heavy 
infestations, or when its cost approaches that of an application of acid, 
then spraying should be practiced. 

14 Asian der, Alfred. Sulphuric acid as a weed spray. Jour. Agr. Research 24(11) ; 
1065-91. 1927. 

14 University of California — Experiment Station 


Experience in France shows that it is sometimes advisable to precede the 
sulfuric acid treatment with a light application of lime, whereas reports 
from England state that the acid application has been found to produce 
little change in the soil acidity. Martin 15 makes the following statement : 
"Results show that the change in acidity of the soil is so small, if indeed 
it exists at all, that no increase in lime is required beyond the amount 
that would normally be applied in the ordinary course of good hus- 
bandry." In California, where most soils are neutral or slightly alkaline, 
the effect, if any, would probably be beneficial. 


The effect of sulfuric acid on the control of grain diseases has not been 
included in this study. Rabate, 16 however, has found it to be effective 
in controlling crown-rot of grain, a disease which causes lodging. Be- 
cause of the lack of competition with weeds, together with the set-back 
received at the time of application, sprayed grain seldom lodges. Figure 
5 shows the condition of the sprayed and unsprayed grain at harvest 
time on the River Farms experiment. Sprayed grain is generally from a 
week to ten days later in reaching maturity than the untreated. 


Dilute sulfuric acid applied as a weed spray has no effect upon the weed 
seeds that are ungerminated in the soil. One year's application, there- 
fore, will not free a field of mustard and wild radish. According to ex- 
periments on buried seeds, mustard seed may germinate after having 
been buried in the soil as long as 40 years. Experience in France, where 
this method of weed control has been in progress for nearly 25 years, 
shows that from 6 to 7 years of repeated sprayings are necessary to free 
a field of these weeds. Since each year's treatment reduces the seed pop- 
ulation considerably, the infestation will probably be reduced, after a 
few years, so that hand-pulling may be more economical than spraying. 


Believing that the usefulness of sulfuric acid as a general herbicide for 
the control of weeds along fence lines, ditchbanks, roadsides, and similar 
waste places, could be increased by the addition of a material that would 
cause the solution to wet the foliage more thoroughly, experimenters 

is Martin, L. D. Spraying weeds in cereal crops with sulphuric acid. Jour. Min. 
Agr. [Gt. Brit.] 40:1129-35. March, 1934. 

!« Rabate, E. The use of sulphuric acid against weeds and certain crop parasites. 
Internatl. Rev. Sci. and Pract. Agr. [Rome] (n.s.) 4:535-45. 1926. 

Bul. 596] 

Sulfuric Acid for Control of Weeds 


have tested many so-called "spreaders." A method developed by O'Kane, 
Westgate, Glover, and Lowry, 17 modified somewhat to meet our condi- 
tions and equipment, has been utilized in these tests. This method con- 
sists primarily of measuring the "angle of contact" that a drop of liquid 
makes with a solid. A small angle indicates that the droplet is flattened, 
hence covers greater surface. For a given liquid and a given solid, the 

r°er certf cas?ce/7tra/.'s>/7 

Fig. 7, 

-The relative contact performance of several wetting agents or "spreaders" 
in 10 per cent sulfuric acid on waxed glass. 

angle is constant, provided the droplets are small and the rate of evap- 
oration is not great. When droplets of 10 per cent acid containing differ- 
ent concentrations of wetting agents had been placed on waxed bottles, 
the image of the droplet was projected, and the angle of contact meas- 
ured. The waxed surfaces were formed on bottles by dipping them into 
a supersaturated solution of beeswax in carbon tetrachloride. These 
surfaces were uniform and, in addition, fairly resistant to spreading 
liquids, thus permitting the study of higher concentrations of spreaders. 
The results of these tests are shown graphically in figure 7. Dilute sul- 
furic acid without the addition of a spreader forms an angle of contact 
with waxed bottles greater than 90 degrees. 

Certain field tests with a wetting agent have shown that the effective- 

17 O'Kane, W. C, W. A. Westgate, L. C. Glover, and P. E. Lowry. Surface ten- 
sion, surface activity, and wetting ability as factors in the performance of contact 
insecticides. New Hampshire Agr. Exp. Sta. Tech. Bul. 39:1-44. 1930. 


University of California — Experiment Station 

ness was much greater than when the acid alone was used. Plants with 
waxy leaf surfaces are often not injured by the acid spray, whereas the 
addition of a spreader often kills them. Grasses, however, though badly 
scorched, are not always completely killed by this spray. Water-grass 
(Echinochloa crus-galli) has been sufficiently dried up by the spray to 
allow burning, thus leaving the ground bare. 


Since onions react to dilute sulfuric acid in a manner similar to cereals, 
the control of annual weeds by spraying the growing crop with this ma- 
terial has been tried. The onion crop treated was heavily infested with 
knotgrass (Polygonum aviculare ) , a weed rather easily killed by the acid. 

Fig. 8. — Onions 24 hours after a spraying with 10 per cent sulfuric acid. 
Unsprayed rows infested with knotgrass (Polygonum aviculare) are shown in 
the foreground. 

In early trials with a knapsack sprayer, 10 per cent acid by weight was 
found to be very successful ; and, though the onions were badly scorched 
for several days after treatment, they recovered completely within two 
weeks (fig. 8). Application of the spray with power equipment on this 
same field later in the season did not give a complete control of the weeds, 
and the injury to the onions appeared greater. It would seem advisable, 
then, as in spraying cereals, to apply the acid when both onions and 
weeds are young. 

In some cases in these experiments a spreader was used, but without 

Bul. 596] Sulfuric Acid for Control of Weeds 17 

marked differences in results. The injury to the onions was only slightly 
greater when the spreader was used and the knotgrass was killed by the 
spray both with and without the addition of the wetting agent. 


Effect of Sulfuric Acid on Metals and Other Materials. — In the United 
States the use of dilute sulfuric acid as a herbicide has been retarded 
largely by lack of sprayers that will resist corrosion. Some materials, 
such as brass, bronze of low zinc content, rubber, and steel withstand 
the effects of the acid very well under certain conditions. The concen- 
trated acid can be handled, for example, in steel drums and iron or 
Everdur 18 pipe, but will rapidly attack rubber hose. The dilute acid can 
be handled in either Everdur pipe or rubber spray hose but will quickly 
corrode steel and wrought iron. Nickel will resist the effect of either 
dilute or concentrated acid but is too expensive to use except for such 
parts as nozzle disks. Though present knowledge of acid-resistant mate- 
rials is very extensive, manufacturers in this country have not been 
willing to guarantee a pump made of any material to apply dilute sul- 
furic acid satisfactorily under field conditions. The common acid-resist- 
ant materials are limited to such uses as piping, nozzles, and stationary 
parts of an acid-handling system. 

Avoiding Open Handling of Sulfuric Acid. — The use of acid is not 
dangerous if a few facts are kept in mind : it is safe, for example, to pour 
concentrated acid into water ; but if water is poured into concentrated 
acid, heat is generated very rapidly, and the sputtering and splattering 
that occurs might cause serious burns to the person doing the mixing. 
Handling this chemical in the open always involves the danger of acid 
burns, which are rather obstinate in healing. The acid, also, whether in 
dilute or concentrated form is very destructive to the shoes and other 
clothing worn by the operator. 

Concentrated sulfuric acid is heavy ; commercial 66° Baume acid has 
a specific gravity of 1.84, a gallon weighing 15.3 pounds. Commercial 
acid is generally shipped in 50 and 100-gallon drums, the total weight 
when full being approximately 1,700 pounds for a 100-gallon, and 900 
pounds for a 50-gallon drum. Obviously, handling the acid drums is 
difficult unless some mechanical device is provided to hoist or roll drums 
into place. 

For the reasons just mentioned, it is desirable to handle acid as little 
as possible ; furthermore, considerable time is consumed in transferring 
acid from drums to sprayer tanks. If concentrated acid is mixed with 
water in open tanks, either the amount of acid has to be measured or the 

!8 Everdur is a copper-silicon-manganese alloy. 


University of California — Experiment Station 

dilute mixture must be tested by the specific-gravity method to deter- 
mine the concentration. This is a time-consuming and rather disagree- 
able task. Valves, faucets, or gear pumps, when used to draw concen- 
trated acid from drums, soon corrode so that their operation becomes 

****-^A0J**> /Area 

6 /2//3G fAreedfc 

Fig. 9. — Penberthy No. 62, %-inch steam ejector used on experimental sprayer 
for mixing concentrated acid and water. 

difficult. Considering the problems presented by concentrated acid, it is 
desirable to eliminate all handling except in closed drums. Such a 
method has been developed. 

Development of Ejector Mixing Method. 12 — The object in developing 
a sprayer for sulfuric acid was to eliminate the necessity of handling 
concentrated acid and also of pumping the dilute acid. Possibly some 
acid-resistant materials could be obtained for constructing a pump to 
handle dilute sulfuric acid, but the pump would probably be too expen- 
sive for agricultural use. It seemed desirable, furthermore, to use ordi- 

1 9 French, O. C, and W. E. Ball. A study of suitable equipment for applying 
sulphuric acid for weed control. Agr. Engin. 15:411-13. 1934. 

Bul. 596] 

Sulfuric Acid for Control of Weeds 


nary orchard sprayers that are now available by adding a field-spray 
boom, by providing an arrangement for carrying concentrated acid, 
and by installing an acid-injecting device in the water-discharge line 
from the pump. The use of an injecting device would then allow the 
pump to handle only water. 

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tyra/ 6oom 

Fig. 10. — Schematic plan of experimental setup used in the development of the 
ejector acid-mixing method. 

The injecting device originally suggested was a specially designed 
brass Venturi tube. After some preliminary trials comparing a Pen- 
berthy bronze ejector (fig. 9) with the Venturi tube, the latter was 
abandoned because one of suitable size was not commercially available, 
whereas the ejectors can be purchased from plumbing dealers for a 
nominal sum. 

In the experiments with the ejector on a portable orchard sprayer, a 
set-up was used as illustrated in figure 10. The sprayer had a triplex 
pump with a capacity of about 16 gallons per minute. A boom 16 feet 
long fitted with Hummer nozzles 20 containing No. 4 disks was connected 
to the discharge line from the pump. In the discharge pipe, at a point 
3 feet from the boom, a No. 62 Penberthy %-inch ejector was installed. 
A %-inch pipe, placed in a container for the concentrated acid, was con- 

20 Known also as Chipman nozzles. 


University of California — Experiment Station 

nected to the low-pressure side of the ejector. A union was placed in this 
%-inch pipe to hold nickel disks with round-hole orifices to control the 
amount of acid drawn into the ejector. With this arrangement the pump 
and piping system handled only water up to the ejector. A sufficient 
number of nozzles were placed on the boom to create the necessary 
pressure differential between the pump and the boom to develop less 










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So 6o ro so 

Fig. 11. — The range of concentration of sulfuric acid obtained with a Penberthy 
ejector by varying the pressure and the number of nozzles on the spray boom. 

than atmospheric pressure at the suction side of the ejector. The acid 
concentration of the dilute solution discharged from the boom was de- 
termined by catching samples from the nozzles and obtaining the spe- 
cific gravity of the solution by means of a hydrometer. When checked by 
weighing the intake of acid, this method proved to be sufficiently accu- 
rate for ordinary field spraying. By means of samples taken at different 
nozzles on the boom, the uniformity of mixture was confirmed. 

The concentration of the solution was determined for varying rates 
of discharge for three sizes of orifices in the ejector suction line — namely, 
■/4> %6> and Y$ inch diameter. For each orifice tested, nine rates of dis- 
charge were obtained by using pressures at the boom nozzles of 52, 62, 
and 72 pounds per square inch for 9, 10, and 11 nozzles equipped with 
No. 4 disks. 

The results of these tests to determine the range of concentration re- 

Bul. 596] Sulfuric Acid for Control of Weeds 21 

suiting from change in pressure and number of nozzles are shown in 
figure 11. For a No. 62 ejector, according to these data, acid concentra- 
tions from as low as 2.0 per cent by weight to as high as 16.5 per cent 
could be obtained by changing the size of the suction orifice and the 
quantity of spray-boom discharge. Ordinarily the acid concentration 
could be varied through a great enough range by simply changing the 
suction orifice. The concentrated acid mixed almost instantaneously 

Fig. 12. — Field-sprayer unit for spraying sulfuric acid. Note the 
alternate tilting of nozzles. 

with the water in the throat of the ejector. Since the viscosity of con- 
centrated acid varies greatly with temperature, this factor was at first 
expected to complicate the problem. Concentrated acid varying in tem- 
perature from 46° to 104° F was run through the ejector; the concen- 
trations determined at the nozzles showed a variation of less than 1 per 
cent which, for this work is insignificant. Likewise, it seemed that a 
difference might result in acid concentration as the level in the concen- 
trated-acid container was lowered. Tests, however, showed that under 
ordinary conditions pressure at the ejector was sufficiently reduced so 
that a difference of 2 or 3 feet in suction lift resulted in a negligible 
variation in acid concentration. 

Equipment Used in 1935. — In order that the ejector mixing method 
developed in the preliminary experiments might be used under actual 
field conditions, there was assembled for use in 1935 a spray unit capable 
of applying the acid in a commercial manner. 

A portable orchard sprayer (with a power take-off), capable of de- 
livering 20 gallons per minute, was selected as the basic machine. This 
unit was equipped with a standard 400-gallon metal tank and mounted 


University of California — Experiment Station 

on dual 6.00 x 20 inch pneumatic tires. On the rear of this sprayer a 
frame was built that held a 50-gallon drum of concentrated sulfuric 
acid and also supported an 18-foot folding boom (fig. 12) . 

The boom was made of Everdur pipe, in three sections. The center sec- 
tion was of %-inch pipe, 6 feet long. The two outer sections, each 6 feet 
long, were of Vi-hich pipe, being connected to the center section with 
short lengths of rubber spray hose so that they could be folded in to the 

Fig. 13. — Eear view of sprayer, showing boom folded for transportation. 

center. When folded, the boom (fig. 13) had an over-all length of ap- 
proximately 7 feet, facilitating transportation and the moving of the 
rig through narrow gates. Twenty Hummer nozzles with special nickel 
disks that discharged fan-shaped spray of approximately 65° included 
angle were placed equidistant on the boom to obtain an approximate 
width of 19 feet of spray. With the boom 2 feet above the foliage, this 
arrangement of nozzles gave a double coverage. The nozzles were con- 
nected to the boom by means of two street-ell pipe fittings in order that 
the spray could be directed either slightly ahead or to the rear of the 
boom (fig. 12). By tilting alternate nozzles, a more thorough coverage is 
possible. To insure uniform pressure throughout the boom, provision 
was made for the dilute acid mixture to enter at two places in the center 
section of the boom by means of rubber hoses. A gauge was connected to 
the boom to register pressure of the dilute acid. A No. 62 Penberthy 
ejector was attached to the water discharge line from the spray pump at 
the rear of the water tank (fig. 14a). Immediately ahead of the ejector 

Bul. 596] 

Sulfuric Acid for Control, of Weeds 


on the water line, a quick-opening gate valve and also a pressure gauge 
were installed (fig. 14, b and e). A %-inch pipe was connected to the 
suction side of the ejector and then placed through the plug of the con- 
centrated-acid drum (fig. 15) . The plug was drilled slightly larger than 
the outside diameter of the %-inch pipe. In this pipe line another quick- 
opening gate valve and a union were installed (fig. 15, a and b). The 

Fig. 14. — Side view of piping system: a, ejector; b, water cut- 
off valve ; c, pipe carrying concentrated sulfuric acid to the ejector ; 
d, pipe carrying dilute solution of acid to the boom; e, pressure 
gauge on the water line. 

union allowed the piping to be disconnected so that acid drums could 
be readily removed. This union contained a thin nickel disk with an 
orifice in it to control the amount of acid drawn into the ejector. The cut- 
off valve on this line was necessary to keep water from being forced 
back into the acid tank through the ejector when the valve on the water 
line was closed. Everdur pipe was used from the valve on the acid-suc- 
tion line to the boom. The pipe in the acid drum and to the valve was 
ordinary black iron. 

In order to lift the 50-gallon drum of concentrated acid up into place, 
a small winch was built on the frame just behind the water tank. When 
the two chains on the winch were placed under the acid drum, the drum 
could easily be raised into the frame and fastened with strap-iron hang- 
ers (fig. 15c). 


University of California — Experiment Station 

A small tractor of track-layer type with a power take-off was used to 
pull and to supply power for the sprayer. A track-layer tractor seemed 
desirable because of the soft fields ordinarily encountered during the 
spray season. 

Tests of the 1935 Sprayer. — According to preliminary experiments, 
probably only three different concentrations of dilute acid are required 

Fig. 15. — View showing piping system : a, union to hold acid-control disk ; 
b, concentrated acid cut-off valve ; c, Avinch for raising acid drum into place ; d, 
ejector suction pipe through bung of concentrated acid drum. The bung is pro- 
vided with a i/L-inch air vent. 

for most spray work — namely 8, 10, and 15 per cent by weight. Of these, 
10 per cent is most commonly used. The equipment was designed to give 
these concentrations. Nozzles were used that delivered approximately 
0.65 gallon per minute each, at 70 pounds per square inch pressure, this 
pressure having already been determined as optimum. With 20 nozzles 
on the boom the total discharge was 13 gallons per minute at 70 pounds' 
pressure. Nickel disks with round-hole orifices drilled with Nos. 35, 30, 
and 15 drills for 8, 10, and 15 per cent acid concentrations, respectively, 
were used in the union in the concentrated-acid line. 

For operation of the sprayer the pump was started and the pressure 
regulator adjusted so that the pressure in the boom was about 70 pounds 
when acid was going through the ejector. When the acid valve was 
closed the pressure in the boom would drop about 10 pounds ; this was 
a visible means of determining whether or not acid was being drawn 

Bul. 596] 

Sulfuric Acid for Control of Weeds 


into the ejector. To get 70 pounds' pressure in the boom it was necessary 
to have about 225 pounds' pressure at the pump or just ahead of the 

The concentration of the diluted acid was determined by the specific- 
gravity method. This consisted of catching a sample of the spray solution 
from one of the nozzles, in a hydrometer jar, and reading the specific 
gravity direct with a hydrometer. By means of a conversion table (table 
4) the specific-gravity reading was converted into percentage of acid 


Amount of Concentrated Sulfuric Acid by Weight and Volume Eequired per 

Hundred Gallons of Water for Various Concentrations 

and the Corresponding Specific Gravity* 

Per cent 

Concentrated acid 

Specific gravity at — 




20° C 

25° C 

30° C 

40° C 




3 46 

4 74 
6 70 

8 00 

9 30 

72 5 
92 5 
102 5 

1 0317 
1 0453 
1 0522 
1 0661 
1 0731 
1 0802 
1 0947 
1 1020 












9 .. . 














* National Research Council of the United States of America. International critical tables of numer- 
ical data, physics, chemistry and technology 3:56. McGraw-Hill Book Co., Inc. New York City. 1928. 

concentration. For this work a relatively inexpensive hydrometer grad- 
uated from 1.000 to 1.200 in 0.005 subdivisions was satisfactory. A glass 
hydrometer jar l 1 /^ inches in diameter and 12 inches high proved con- 
venient for protecting the hydrometer stem from the wind. 

As experiments have proved, the volume of dilute acid solution re- 
quired per acre is approximately 125 to 135 gallons when a 10 per cent 
concentration is used ; 90 to 100 gallons for 15 per cent ; and 150 to 170 
gallons for an 8 per cent solution. 

To apply any definite volume of material per acre it is necessary to 
know three factors : first, the quantity discharged per minute from the 
boom; second, the width of strip that the spray from the boom will 
cover ; and third, the rate of travel through the field. The sprayer used 
for this study, as stated previously, delivered 13 gallons per minute at 
optimum pressure and covered a strip 19 feet wide. With a tractor 
whose field speeds were 2, 2.6, and 3.6 miles per hour, the volume of 

26 University of California — Experiment Station 

spray applied per acre was 170, 130, and 95 gallons for low, intermedi- 
ate, and high gear respectively. 

Grain fields were sprayed with this equipment at the rate of from 4% 
acres per hour in low gear to 8 acres per hour in high gear. When water 
was readily available, from 40 to 50 acres could easily be sprayed in a 
ten-hour day. 

Water pumped directly out of ditches into the sprayer tank was used 
in many of the tests. As there was an 18 mesh-to-the-inch screen in the 
water-discharge line, very little trouble with nozzles' clogging was ex- 
perienced. Proper servicing of this screen is essential because the small 
nozzles will clog unless good screening of the water is obtained. If the 
screens supplied with sprayers do not fit tightly against the castings in 
the screen bowl, gaskets must be placed between the screen cage and the 
bowl-opening plate. 

Conversion of a Portable Orchard Sprayer to an Acid Sprayer. — To 
use the ejector system of mixing acid and water it is necessary to main- 
tain a rather definite relation between the water pressure ahead of the 
ejector and the amount of pressure in the boom. A pressure drop of ap- 
proximate 150 pounds per square inch through the ejector must occur 
in order to reduce pressure on the suction side of the ejector sufficiently 
to cause acid to flow in the suction line. Unless the boom has sufficient 
capacity to allow this pressure drop to occur, the ejector will not func- 
tion properly. The most practical size of ejector is the No. 62 Penberthy 
or one corresponding very closely to its specifications. The dimensions of 
this ejector are shown in figure 9. 

To utilize this ejector it is necessary to have a pump that delivers at 
least 16 gallons per minute at 200 pounds pressure per square inch. 
Many triplex portable orchard sprayers have this capacity or more. The 
sprayer should have at least a 300 and preferably a 400-gallon tank for 
water. More than 400 gallons' capacity would be desirable except that 
the additional weight is a disadvantage when the spray rig is being 
pulled through a grain field, which is apt to be soft during the spray 

A boom with 20 nozzles, of the flat, fan-shaped spray type, that will 
cover a strip 19 to 20 feet wide, is about the optimum size. Each nozzle 
should deliver approximately 0.65 gallon per minute at 70 pounds 
pressure per square inch. If the nozzles are spaced 12 inches apart on 
the boom an effective spray giving double coverage will be obtained. The 
boom should be adjustable for height; 18 inches above the ground is 
about as low as is ever necessary, and 27 inches is a maximum height for 
most grain-field work. The boom should be made of Everdur or brass pipe 

Bul. 596] Sulfuric Acid for Control of Weeds 27 

and fittings ; nozzles should be of similar material with nickel or monel- 
metal disks. All pipe from the ejector to the boom and from the valve on 
the acid-suction line to the ejector must likewise be acid resistant. Brass 
pipe should not be used in the concentrated acid drum ; black iron pipe 
is more satisfactory. A gasket-type union placed somewhere between the 
acid drum and the valve on the acid-suction line is convenient for hold- 
ing the orifice disk that controls the amount of concentrated acid flowing 
to the ejector. The size of hole to drill in the acid-control disk will prob- 
ably vary slightly with each individual sprayer. A simple way to de- 
termine the size of hole in the disk necessary to give a desired acid con- 
centration is to start with the size given above under "Tests of the 1935 
Sprayer" and then to check the acid concentration with a hydrometer. 
If this does not quite meet the requirements, change the drill size accord- 
ingly, and recheck the specific gravity of the dilute solution coming 
from the nozzle until the desired concentration is obtained. The specific 
gravity of various acid concentrations is shown in table 4. 

A pressure gauge should be placed on the boom so that it is visible to 
the operator. An ordinary gauge with a range from to 100 pounds is 
suitable. The gauge should be mounted on a goose-neck pipe filled with oil 
so that the acid solution will not damage the gauge. Such an arrange- 
ment can be seen in figure 14. 

This bulletin does not give exact specifications for building every 
sprayer of this type, but rather gives general specifications and some 
details that will be required on any sprayer of sulfuric acid. Many modi- 
fications of the equipment described in this bulletin will doubtless be 
made by those building spray rigs. 

Cost of Application of Acid. — Costs for spraying grain fields vary 
greatly according to the amount of acid necessary, the cost of the acid, 
and the distance of water from the spraying operations. The cost of acid 
in 1935 was $1.40 per hundred pounds in 100-gallon lots. The amount 
required per acre depends largely on the size of mustard ; in general, 10 
per cent concentration is satisfactory, or 6.05 gallons per acre, making a 
cost of $1.50 per acre for acid. Water costs vary with the equipment 
necessary to supply the water to the sprayer and also with the distance 
that water must be transported. 

The cost of materials necessary to convert an orchard sprayer to a 
field-type sprayer should not be over $100.00, including labor. At present 
prices, apparently a charge of $1.50 per acre for machinery and labor 
should be ample, making the total cost of application per acre approxi- 
mately $3.00. 

28 University of California — Experiment Station 


The few precautions required in handling sulfuric acid are simple, but 
important. First, though the action of concentrated acid on steel drums 
is hardly noticeable, the acid does react slightly with the metal after 
standing for a few months in the drum, and free hydrogen is liberated. 
Hydrogen is inflammable ; if a flame were exposed near a recentty opened 
drum partly filled with acid, an explosion might result. For this reason 
it is always best never to have a flame near a drum of acid from which 
the plug has just been removed. Second, drums of concentrated acid 
should never be left lying exposed to hot sunlight with the plug fitting 
tightly. The acid will expand, and the pressure might burst the drum. If 
the drum is partly filled with the acid it is more dangerous than when 
full because the air becomes compressed within the drum ; a fault in the 
drum would produce an explosion. Third, to obtain the longest possible 
life of equipment it is advisable to flush out the boom with water after 
each day's spraying. Fourth, the operator should wear old clothes ; wool- 
ens are more resistant to the acid than cotton fabrics. Rubber clothing 
gives even more effective protection, but is expensive. Leather shoes are 
readily attacked by the acid, hence rubber boots should be worn. As an 
additional safeguard, goggles might be worn to protect the eyes from 
the acid spray. Fifth, an operator of an acid sprayer should always have 
a solution of water and bicarbonate of soda (baking soda) readily avail- 
able to neutralize any acid that may come in contact with his body. 


For a number of years, sulfuric acid has been used in controlling annual 
weeds, particularly mustard and wild radish in grain fields. In France, 
500,000 acres of cereals were sprayed with sulfuric acid in 1933 ; while 
in England, in 1934, over 20,000 acres of grain were sprayed. 

Of the 1,475,000 acres of small grain grown in California in 1935, 
approximately 50 per cent was infested with weeds that may be con- 
trolled with sulfuric acid. 

The lack of suitable equipment for applying dilute sulfuric acid has 
retarded the use of that chemical as a herbicide in the United States. 
After two years of experimental work, however, a successful sprayer 
has been developed. The use of an ejector mixing device eliminates the 
necessity not only of having dilute acid in contact with a spray pump 
but also of mixing the acid in open containers. 

According to experimental results, approximately 95 per cent of the 
mustard and wild radish in grain fields may be controlled with dilute 
sulfuric acid. Sprayed plots have often produced 50 per cent more grain 
than unsprayed plots. 

Bul. 596] Sulfuric Acid for Control of Weeds 29 

The concentration of the acid and the volume of solution per acre may 
vary with climatic conditions ; but in general 10 per cent acid by weight, 
applied at the rate of 130 gallons per acre, has given best results. 

Under the conditions of these experiments the total cost of an applica- 
tion has been approximately $3.00 per acre. 


The authors are grateful to the John Bean Mfg. Company and the Cater- 
pillar Company for furnishing equipment used in the 1935 experiments ; 
and to the Stauffer Chemical Company for supplying sulfuric acid.